Light-Emitting Element, Light-Emitting Device, Electronic Device, and Lighting Device

ABSTRACT

A light-emitting element with high reliability that can keep favorable characteristics after long-time driving is provided. In addition, a light-emitting device having a long lifetime including the light-emitting element is provided. Moreover, an electronic device and a lighting device having a long lifetime are provided. In a light-emitting element including an EL layer between a pair of electrodes, a light-emitting layer included in the EL layer has a stacked-layer structure which is different from the conventional structure, whereby the light-emitting element can keep favorable characteristics after long-time driving even in the case where carrier balance is changed over time due to driving of the light-emitting element or a light-emitting region is shifted due to the change.

This application is a continuation of copending U.S. application Ser.No. 15/186,807, filed on Jun. 20, 2016 which is a continuation of U.S.application Ser. No. 14/513,982, filed on Oct. 14, 2014 (now U.S. Pat.No. 9,379,345 issued Jun. 28, 2016) which are all incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. In particular, oneembodiment of the present invention relates to a semiconductor device, adisplay device, a light-emitting device, a lighting device, drivingmethods thereof, or manufacturing methods thereof. In particular, oneembodiment of the present invention relates to a light-emitting elementin which an organic compound that emits light by application of anelectric field is provided between a pair of electrodes, and alsorelates to a light-emitting device, an electronic device, and a lightingdevice including such a light-emitting element.

2. Description of the Related Art

A light-emitting element using an organic compound as a luminous body,which has features such as thinness, lightness, high-speed response, andDC drive at low voltage, is expected to be used in a next-generationflat panel display. In particular, a display device in whichlight-emitting elements are arranged in matrix is considered to haveadvantages in a wide viewing angle and excellent visibility over aconventional liquid crystal display device.

It is said that the light emission mechanism of a light-emitting elementis as follows: when a voltage is applied between a pair of electrodeswith an EL layer including a luminous body provided therebetween,electrons injected from the cathode and holes injected from the anoderecombine in the light emission center of the EL layer to form molecularexcitons, and energy is released and light is emitted when the molecularexcitons relax to the ground state. Singlet excitation and tripletexcitation are known as excited states, and it is thought that lightemission can be achieved through either of the excited states.

In order to improve element characteristics of such light-emittingelements, improvement of an element structure, development of amaterial, and the like have been actively carried out (for example, seePatent Document 1).

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2010-182699

SUMMARY OF THE INVENTION

In development of a light-emitting element, the reliability is one ofthe important factors in evaluation of the light-emitting element. Evenif the characteristics of the light-emitting element in the initialstage are favorable, in the case where the light-emitting element cannotwithstand long-time driving and the lifetime as an element is short, theutility value is low and the commercialization is difficult. Thus, it isdesirable to develop a light-emitting element which can keep thefavorable characteristics in the initial stage and can withstand drivingas long as possible.

One embodiment of the present invention provides a light-emittingelement with high reliability which can keep favorable characteristicsafter long-time driving. Another embodiment of the present inventionprovides a light-emitting device having a long lifetime in which thelight-emitting element is used. Another embodiment of the presentinvention provides an electronic device and a lighting device each ofwhich has a long lifetime. Another embodiment of the present inventionprovides a novel light-emitting element, a novel light-emitting device,or the like. Note that the descriptions of these objects do not disturbthe existence of other objects. In one embodiment of the presentinvention, there is no need to achieve all the objects. Other objectswill be apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a light-emitting elementincluding an EL layer between a pair of electrodes. A light-emittinglayer included in the EL layer has a stacked-layer structure which isdifferent from the conventional structure, whereby the light-emittingelement can keep favorable characteristics after long-time driving evenin the case where carrier balance is changed over time due to driving ofthe light-emitting element or a light-emitting region is shifted due tothe change.

Specifically, in the case where the light-emitting layer included in theEL layer of the light-emitting element has a stacked-layer structure andthe stacked light-emitting layers contain different light-emittingmaterials, a light-emitting layer having the same structure as that of alight-emitting layer that contains a light-emitting material exhibitingemission at a short wavelength is further provided, and a light-emittinglayer that contains a light-emitting material exhibiting emission at along wavelength is sandwiched between the two light-emitting layers eachof which contains a light-emitting material exhibiting emission at ashort wavelength. As a result, even in the case where the light-emittingregion is shifted due to the change in carrier balance in each stackedlight-emitting layer or between the light-emitting layers, anotherlight-emitting layer can compensate for the change and the stable statein the whole light-emitting layer can be kept; thus, a light-emittingelement that can keep the favorable characteristics after long-timedriving can be obtained.

Thus, one embodiment of the present invention is a light-emittingelement including an EL layer including at least a light-emitting layerbetween a pair of electrodes. The light-emitting layer includes alight-emitting material, a hole-transport material, and anelectron-transport material, and has a stacked-layer structure of afirst light-emitting layer, a second light-emitting layer, and a thirdlight-emitting layer from an anode side. Light emission obtained fromthe first light-emitting layer and light emission obtained from thethird light-emitting layer has the same light emission color and isexhibited at a shorter wavelength than light emission obtained from thesecond light-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. The light-emitting materials of the first light-emittinglayer and the third light-emitting layer are the same and have anemission peak at a shorter wavelength than that of the secondlight-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. The hole-transport materials of the first light-emittinglayer, the second light-emitting layer, and the third light-emittinglayer are the same, and the electron-transport materials of the firstlight-emitting layer, the second light-emitting layer, and the thirdlight-emitting layer are the same. Light emission obtained from thefirst light-emitting layer and light emission obtained from the thirdlight-emitting layer has the same light emission color and is exhibitedat a shorter wavelength than light emission obtained from the secondlight-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. The hole-transport materials of the first light-emittinglayer, the second light-emitting layer, and the third light-emittinglayer are the same, and the electron-transport materials of the firstlight-emitting layer, the second light-emitting layer, and the thirdlight-emitting layer are the same. The light-emitting materials of thefirst light-emitting layer and the third light-emitting layer are thesame and have an emission peak at a shorter wavelength than that of thesecond light-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. A combination of the hole-transport material and theelectron-transport material in the light-emitting layer forms anexciplex. Light emission obtained from the first light-emitting layerand light emission obtained from the third light-emitting layer has thesame light emission color and is exhibited at a shorter wavelength thanlight emission obtained from the second light-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. A combination of the hole-transport material and theelectron-transport material in the light-emitting layer forms anexciplex. The light-emitting materials of the first light-emitting layerand the third light-emitting layer are the same and have an emissionpeak at a shorter wavelength than that of the second light-emittinglayer.

Another embodiment of the present invention is the light-emittingelement in which the hole-transport materials of the firstlight-emitting layer, the second light-emitting layer, and the thirdlight-emitting layer are the same and the electron-transport materialsof the first light-emitting layer, the second light-emitting layer, andthe third light-emitting layer are the same in each of the abovestructures including the hole-transport material and theelectron-transport material in the light-emitting layer.

Another embodiment of the present invention is the light-emittingelement in which the light-emitting material included in thelight-emitting layer is a substance emitting phosphorescence in each ofthe above structures.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. A weight proportion of the hole-transport material to theelectron-transport material in the first light-emitting layer and thethird light-emitting layer is lower than or equal to 50%, and a weightproportion of the hole-transport material to the electron-transportmaterial in the second light-emitting layer is lower than or equal tothe weight proportion of the hole-transport material to theelectron-transport material in the first light-emitting layer and thethird light-emitting layer. Light emission obtained from the firstlight-emitting layer and light emission obtained from the thirdlight-emitting layer has the same light emission color and is exhibitedat a shorter wavelength than light emission obtained from the secondlight-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding an EL layer including at least a light-emitting layer betweena pair of electrodes. The light-emitting layer includes a light-emittingmaterial, a hole-transport material, and an electron-transport material,and has a stacked-layer structure of a first light-emitting layer, asecond light-emitting layer, and a third light-emitting layer from ananode side. A weight proportion of the hole-transport material to theelectron-transport material in the first light-emitting layer and thethird light-emitting layer is lower than or equal to 50%, and a weightproportion of the hole-transport material to the electron-transportmaterial in the second light-emitting layer is lower than or equal tothe weight proportion of the hole-transport material to theelectron-transport material in the first light-emitting layer and thethird light-emitting layer. The light-emitting materials of the firstlight-emitting layer and the third light-emitting layer are the same andhave an emission peak at a shorter wavelength than that of the secondlight-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding a plurality of EL layers between a pair of electrodes, and acharge generation layer between the adjacent EL layers. The EL layerincludes at least a light-emitting layer. The light-emitting layerincludes a light-emitting material, a hole-transport material, and anelectron-transport material, and has a stacked-layer structure of afirst light-emitting layer, a second light-emitting layer, and a thirdlight-emitting layer from an anode side. Light emission obtained fromthe first light-emitting layer and light emission obtained from thethird light-emitting layer has the same light emission color and isexhibited at a shorter wavelength than light emission obtained from thesecond light-emitting layer.

Another embodiment of the present invention is a light-emitting elementincluding a plurality of EL layers between a pair of electrodes, and acharge generation layer between the adjacent EL layers. The EL layerincludes at least a light-emitting layer. The light-emitting layerincludes a light-emitting material, a hole-transport material, and anelectron-transport material, and has a stacked-layer structure of afirst light-emitting layer, a second light-emitting layer, and a thirdlight-emitting layer from an anode side. The light-emitting materials ofthe first light-emitting layer and the third light-emitting layer arethe same and have an emission peak at a shorter wavelength than that ofthe second light-emitting layer.

Another embodiment of the present invention is the light-emittingelement in which at least one of the plurality of EL layers emitsdifferent color light in each of the structures including the pluralityof EL layers between the pair of electrodes.

Another embodiment of the present invention is a light-emitting devicethat includes a light-emitting element including an EL layer between areflective electrode and a transflective electrode. The EL layerincludes at least a light-emitting layer. The light-emitting layerincludes a light-emitting material, a hole-transport material, and anelectron-transport material, and has a stacked-layer structure of afirst light-emitting layer, a second light-emitting layer, and a thirdlight-emitting layer from an anode side. The light-emitting elementincludes at least a first light-emitting element in which light emissionis obtained from the first light-emitting layer and the thirdlight-emitting layer and a second light-emitting element in which lightemission is obtained from the second light-emitting layer, and the lightemission obtained from the first light-emitting element is exhibited ata shorter wavelength than light emission obtained from the secondlight-emitting element.

Another embodiment of the present invention is a light-emitting devicethat includes a light-emitting element including an EL layer between areflective electrode and a transflective electrode. The EL layerincludes at least a light-emitting layer. The light-emitting layerincludes a light-emitting material, a hole-transport material, and anelectron-transport material, and has a stacked-layer structure of afirst light-emitting layer, a second light-emitting layer, and a thirdlight-emitting layer from an anode side. The light-emitting materials ofthe first light-emitting layer and the third light-emitting layer arethe same and have an emission peak at a shorter wavelength than that ofthe second light-emitting layer. The light-emitting element includes atleast a first light-emitting element in which light emission is obtainedfrom the first light-emitting layer and the third light-emitting layerand a second light-emitting element in which light emission is obtainedfrom the second light-emitting layer.

Another embodiment of the present invention is a light-emitting devicethat includes a light-emitting element including an EL layer between apair of electrodes. The EL layer includes at least a light-emittinglayer. The light-emitting layer includes a light-emitting material, ahole-transport material, and an electron-transport material, and has astacked-layer structure of a first light-emitting layer, a secondlight-emitting layer, and a third light-emitting layer from an anodeside. Light emission obtained from the first light-emitting layer andlight emission obtained from the third light-emitting layer has the samelight emission color and is exhibited at a shorter wavelength than lightemission obtained from the second light-emitting layer. Thelight-emitting element includes at least a first light-emitting elementin which first light emission is obtained through a first color filterand a second light-emitting element in which second light emission isobtained through a second color filter.

Another embodiment of the present invention is a light-emitting devicethat includes a light-emitting element including an EL layer between apair of electrodes. The EL layer includes at least a light-emittinglayer. The light-emitting layer includes a light-emitting material, ahole-transport material, and an electron-transport material, and has astacked-layer structure of a first light-emitting layer, a secondlight-emitting layer, and a third light-emitting layer from an anodeside. The light-emitting materials of the first light-emitting layer andthe third light-emitting layer are the same and have an emission peak ata shorter wavelength than that of the second light-emitting layer. Thelight-emitting element includes at least a first light-emitting elementin which first light emission is obtained through a first color filterand a second light-emitting element in which second light emission isobtained through a second color filter.

Another embodiment of the present invention is a light-emitting devicein which one electrode of the light-emitting element is formed bystacking a transparent conductive film over a reflective electrode, andthe first light-emitting element and the second light-emitting elementhave different thicknesses of the transparent conductive film in each ofthe structures including the plurality of light-emitting elements.

Another embodiment of the present invention is a light-emitting deviceincluding the light-emitting element having any of the above-describedstructures.

Other embodiments of the present invention are not only a light-emittingdevice including the light-emitting element but also an electronicdevice and a lighting device each including the light-emitting device.Accordingly, a light-emitting device in this specification refers to animage display device, or a light source (including a lighting device).In addition, the light-emitting device might include any of thefollowing modules in its category: a module in which a connector such asa flexible printed circuit (FPC) or a tape carrier package (TCP) isattached to a light-emitting device; a module having a TCP provided witha printed wiring board at the end thereof; and a module having anintegrated circuit (IC) directly mounted on a light-emitting element bya chip on glass (COG) method.

One embodiment of the present invention can provide a light-emittingelement with high reliability which can keep favorable characteristicsafter long-time driving. Another embodiment of the present invention canprovide a light-emitting device having a long lifetime in which thelight-emitting element is used. Another embodiment of the presentinvention can provide an electronic device and a lighting device each ofwhich has a long lifetime. Another embodiment of the present inventioncan provide a novel light-emitting element, a novel light-emittingdevice, or the like. Note that the descriptions of these effects do notdisturb the existence of other effects. One embodiment of the presentinvention does not necessarily achieve all the effects. Other effectswill be apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a structure of a light-emitting element of oneembodiment of the present invention;

FIGS. 2A and 2B each illustrate a structure of a light-emitting element;

FIG. 3 illustrates structures of light-emitting elements;

FIGS. 4A and 4B illustrate a light-emitting device;

FIGS. 5A to 5D illustrate electronic devices;

FIG. 6 illustrates lighting devices;

FIGS. 7A and 7B illustrate structures of Light-emitting Element 1 andComparative Light-emitting Element 2;

FIG. 8 shows luminance-current efficiency characteristics ofLight-emitting Element 1 and Comparative Light-emitting Element 2;

FIG. 9 shows luminance-external quantum efficiency characteristics ofLight-emitting Element 1 and Comparative Light-emitting Element 2;

FIG. 10 shows voltage-luminance characteristics of Light-emittingElement 1 and Comparative Light-emitting Element 2;

FIG. 11 shows emission spectra of Light-emitting Element 1 andComparative Light-emitting Element 2;

FIG. 12 shows reliability of Light-emitting Element 1 and ComparativeLight-emitting Element 2;

FIGS. 13A and 13B show changes in emission spectra of Light-emittingElement 1 and Comparative Light-emitting Element 2;

FIGS. 14A and 14B illustrate structures of Light-emitting Element 3,Comparative Light-emitting Element 4, Light-emitting Element 5, andComparative Light-emitting Element 6;

FIG. 15 shows luminance-current efficiency characteristics ofLight-emitting Element 3, Comparative Light-emitting Element 4,Light-emitting Element 5, and Comparative Light-emitting Element 6;

FIG. 16 shows voltage-luminance characteristics of Light-emittingElement 3, Comparative Light-emitting Element 4, Light-emitting Element5, and Comparative Light-emitting Element 6;

FIG. 17 shows emission spectra of Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6;

FIG. 18 shows reliability of Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6;

FIG. 19 shows time-chromaticity characteristics of a 3.4-inch activematrix display;

FIGS. 20A and 20B are graphs showing measurement results ofLight-emitting Element 3 by ToF-SIMS;

FIGS. 21A and 21B are graphs showing measurement results ofLight-emitting Element 5 by ToF-SIMS;

FIGS. 22A to 22C are graphs showing measurement results ofLight-emitting Element 3 by ToF-SIMS;

FIGS. 23A and 23B are graphs showing measurement results ofLight-emitting Element 5 by ToF-SIMS; and

FIG. 24 is a graph showing measurement results of Light-emitting Element3 by ToF-SIMS.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be explained below withreference to the drawings. However, the present invention is not limitedto description to be given below, and it is to be easily understood thatmodes and details thereof can be variously modified without departingfrom the purpose and the scope of the present invention. Accordingly,the present invention should not be interpreted as being limited to thecontent of the embodiments below.

Embodiment 1

In this embodiment, a light-emitting element which is one embodiment ofthe present invention will be described.

The light-emitting element of one embodiment of the present invention isformed by providing an EL layer including a light-emitting layer betweena pair of electrodes. The light-emitting layer has a stacked-layerstructure of: a first light-emitting layer including at least a firstlight-emitting material (also referred to as a guest material), anelectron-transport material (also referred to as a host material), and ahole-transport material (also referred to as an assist material); asecond light-emitting layer including at least a second light-emittingmaterial, the electron-transport material, and the hole-transportmaterial; and a third light-emitting layer including at least the firstlight-emitting material, the electron-transport material, and thehole-transport material.

An element structure of the light-emitting element of one embodiment ofthe present invention is described below with reference to FIG. 1.

In the light-emitting element illustrated in FIG. 1, an EL layer 103including a light-emitting layer 106 is provided between a pair ofelectrodes (an anode 101 and a cathode 102), and the EL layer 103 has astructure in which a hole-injection layer 104, a hole-transport layer105, the light-emitting layer 106 (106 a, 106 b, and 106 c), anelectron-transport layer 107, an electron-injection layer 108, and thelike are sequentially stacked over the anode 101.

The light-emitting layer 106 has a stacked-layer structure of aplurality of light-emitting layers (106 a, 106 b, and 106 c). Asillustrated in FIG. 1, a first light-emitting layer 106 a, a secondlight-emitting layer 106 b, and a light-emitting layer 106 c aresequentially stacked over the anode 101. The first light-emitting layer106 a includes at least a first light-emitting material 109 a, anelectron-transport material 110, and a hole-transport material 111. Thesecond light-emitting layer 106 b includes at least a secondlight-emitting material 109 b, the electron-transport material 110, andthe hole-transport material 111. The third light-emitting layer 106 cincludes at least the first light-emitting material 109 a, theelectron-transport material 110, and the hole-transport material 111.

As for the light-emitting materials (the first light-emitting material109 a and the second light-emitting material 109 b) included in thelight-emitting layer 106, the first light-emitting material 109 a isused for the first light-emitting layer 106 a and the thirdlight-emitting layer 106 c, and the second light-emitting material 109 bis used for the second light-emitting layer 106 b. Note that the secondlight-emitting material 109 b has an emission peak wavelength that islonger than that of the first light-emitting material 109 a.

As the electron-transport material 110 included in the light-emittinglayer 106, an organic compound having an electron mobility of greaterthan or equal to 10⁻⁶ cm²/Vs is mainly used, and as the hole-transportmaterial 111, an organic compound having a hole mobility of greater thanor equal to 10⁻⁶ cm²/Vs is mainly used.

When the light-emitting layer 106 has a structure in which thelight-emitting material is dispersed in the electron-transport material110 and the hole-transport material 111, crystallization of thelight-emitting layer 106 can be suppressed. Furthermore, it is possibleto suppress concentration quenching due to high concentration of thelight-emitting material, and thus the light-emitting element can havehigher emission efficiency.

In the stacked light-emitting layers (106 a, 106 b, and 106 c), it ispreferable that the same material be used as the electron-transportmaterials 110 and the same material be used as the hole-transportmaterials 111; however, different materials can be used as long as thelight-emitting layers can function as light-emitting layers.

It is preferable that the level of triplet excitation energy (T1 level)of the electron-transport material 110 (or the hole-transport material111) be higher than the T1 levels of the light-emitting materials (109 aand 109 b). This is because when the T1 level of the electron-transportmaterial 110 (or the hole-transport material 111) is lower than the T1levels of the light-emitting materials (109 a and 109 b), the tripletexcitation energy of the light-emitting materials (109 a and 109 b)contributing to light emission is quenched by the electron-transportmaterial 110 (or the hole-transport material 111), and the emissionefficiency is decreased.

In addition, it is preferable that, in any or all of the stackedlight-emitting layers 106 (106 a, 106 b, and 106 c), a combination ofthe electron-transport material 110 and the hole-transport material 111forms an exciplex. This is because, in this case, the emissionwavelength of the formed exciplex is on the longer wavelength side thanthe emission wavelength (fluorescent wavelength) of each of theelectron-transport material 110 and the hole-transport material 111, andthus fluorescent spectra of the electron-transport material 110 and thehole-transport material 111 can be converted into emission spectra thatare on the longer wavelength side, and the emission efficiency can befurther increased.

In the light-emitting element of one embodiment of the present inventionillustrated in FIG. 1, three light-emitting layers included in the ELlayer are stacked, and the light-emitting layer containing thelight-emitting material exhibiting emission at a long wavelength issandwiched between the two light-emitting layers each of which containsa light-emitting material exhibiting emission at a short wavelength.With such a structure, when the light-emitting element is driven, thecarrier balance in the light-emitting layer is changed over time, andwhen a light-emitting area is shifted to the second light-emitting layer(106 b in FIG. 1) side, the third light-emitting layer (106 c in FIG. 1)can emit light. Thus, when the light-emitting element is driven,degradation of the first light-emitting layer in the initial stage andan increase in luminance of the second light-emitting layer can besuppressed. That is, degradation of the characteristics of the wholelight-emitting layer can be suppressed; thus, the favorablecharacteristics can be kept after long-time driving.

Next, a specific example in manufacturing the above light-emittingelement is described.

As the first electrode (anode) 101 and the second electrode (cathode)102, a metal, an alloy, an electrically conductive compound, a mixturethereof, and the like can be used. Specific examples are indiumoxide-tin oxide (indium tin oxide (ITO)), indium oxide-tin oxidecontaining silicon or silicon oxide, indium oxide-zinc oxide (indiumzinc oxide), indium oxide containing tungsten oxide and zinc oxide, gold(Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd),and titanium (Ti). In addition, an element belonging to Group 1 or Group2 of the periodic table, for example, an alkali metal such as lithium(Li) or cesium (Cs), an alkaline earth metal such as calcium (Ca) orstrontium (Sr), magnesium (Mg), an alloy containing such an element(MgAg, AlLi), a rare earth metal such as europium (Eu) or ytterbium(Yb), an alloy containing such an element, graphene, and the like, canbe used. The first electrode (anode) 101 and the second electrode(cathode) 102 can be formed by, for example, a sputtering method or anevaporation method (including a vacuum evaporation method).

The hole-injection layer 104 injects holes into the light-emitting layer106 through the hole-transport layer 105 with a high hole-transportproperty. The hole-injection layer 104 contains a hole-transportmaterial and an acceptor substance, so that electrons are extracted fromthe hole-transport material by the acceptor substance to generate holesand the holes are injected into the light-emitting layer 106 through thehole-transport layer 105. The hole-transport layer 105 is formed using ahole-transport material.

Specific examples of the hole-transport material, which is used for thehole-injection layer 104 and the hole-transport layer 105, includearomatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB ora-NPD),N,N′-bis(3-methylphenyl)-N,N-diphenyl-[1,1′biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB);3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2); and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylearbazole(abbreviation: PCzPCN1). Other examples include carbazole derivativessuch as 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA).The substances listed here are mainly ones that have a hole mobility of10⁻⁶ cm²/Vs or higher. Note that any substance other than the substanceslisted here may be used as long as the hole-transport property is higherthan the electron-transport property.

A high molecular compound such as poly(N-vinylcarbazole) (abbreviation:PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD) can also be used.

Examples of the acceptor substance that is used for the hole-injectionlayer 104 include transition metal oxides and oxides of metals belongingto Groups 4 to 8 of the periodic table. Specifically, molybdenum oxideis particularly preferable.

The light-emitting layer 106 (106 a, 106 b, and 106 c) is a layercontaining the light-emitting materials (109 a and 109 b). Thelight-emitting layer 106 (106 a, 106 b, and 106 c) described in thisembodiment includes the electron-transport material 110 and thehole-transport material 111 in addition to the light-emitting materials(109 a and 109 b).

There is no particular limitation on the material that can be used asthe light-emitting materials (or emission center substance) (109 a and109 b) in the light-emitting layer 106 (106 a, 106 b, and 106 c). Alight-emitting material that converts singlet excitation energy intoluminescence or a light-emitting material that converts tripletexcitation energy into luminescence can be used. Note that the emissioncolor of the light-emitting material 109 a has a shorter wavelength thanthe emission color of the light-emitting material 109 b. Examples of thelight-emitting material and the emission center substance are givenbelow.

As an example of the light-emitting material that converts singletexcitation energy into luminescence, a substance that emits fluorescencecan be given. Examples of the substance emitting fluorescence includeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tert-butyl)perylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30, N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (abbreviation:2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′Y-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI),{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM).

Furthermore, examples of the light-emitting material converting tripletexcitation energy into luminescence include a substance emittingphosphorescence and a thermally activated delayed fluorescence (TADF)material. Note that “delayed fluorescence” exhibited by the TADFmaterial refers to light emission having the same spectrum as normalfluorescence and an extremely long lifetime. The lifetime is 10⁻⁶seconds or longer, preferably 10⁻³ seconds or longer.

Examples of the substance that emits phosphorescence includebis[2-(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C²′]iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)acetylacetonate (abbreviation: FIracac),tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation:Ir(ppy)₂(acac)), tris(acetylacetonato) (monophenanthroline)terbium(III)(abbreviation: Tb(acac)₃(Phen)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C²′)iridium(III) acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C²′}iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C²′)iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C³′]iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C²′)iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]),(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanate)iridium(III) (abbreviation: [Ir(tppr)₂(dpm)],(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP), tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)₃(Phen)),tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)₃(Phen)), andthe like.

Examples of the TADF material include fullerene, a derivative thereof,an acridine derivative such as proflavine, and eosin. Other examplesinclude a metal-containing porphyrin, such as a porphyrin containingmagnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium(In), or palladium (Pd). Examples of the metal-containing porphyrininclude a protoporphyrin-tin fluoride complex (SnF₂(Proto IX)), amesoporphyrin-tin fluoride complex (SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (SnF₂(Hemato IX)), a coproporphyrintetramethyl ester-tin fluoride complex (SnF₂(Copro III-4Me)), anoctaethylporphyrin-tin fluoride complex (SnF₂(OEP)), anetioporphyrin-tin fluoride complex (SnF₂(Etio I)), and anoctaethylporphyrin-platinum chloride complex (PtCl₂OEP). Alternatively,a heterocyclic compound including a π-electron rich heteroaromatic ringand a π-electron deficient heteroaromatic ring can be used, such as2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(PIC-TRZ). Note that a material in which the π-electron richheteroaromatic ring is directly bonded to the π-electron deficientheteroaromatic ring is particularly preferably used because both thedonor property of the π-electron rich heteroaromatic ring and theacceptor property of the π-electron deficient heteroaromatic ring areincreased and the energy difference between the S₁ level and the T₁level becomes small.

As the electron-transport material 110 used in the light-emitting layer106 (106 a, 106 b, and 106 c), a π-electron deficient heteroaromaticcompound such as a nitrogen-containing heteroaromatic compound ispreferable, examples of which include quinoxaline derivatives anddibenzoquinoxaline derivatives such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[fh]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), and6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II).

As the hole-transport material 111 used in the light-emitting layer 106(106 a, 106 b, and 106 c), a π-electron rich heteroaromatic compound(e.g., a carbazole derivative or an indole derivative) or an aromaticamine compound is preferable, examples of which include4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: DPA2SF),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB), N-(9, 9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N′-phenyl-N′-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2), and3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2).

The electron-transport layer 107 is a layer containing a substance witha high electron-transport property. For the electron-transport layer107, a metal complex such as Alq₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), BAlq,Zn(BOX)₂, or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂) can be used. heteroaromatic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can alsobe used. A high molecular compound such as poly(2,5-pyridinediyl)(abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py) orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can also be used. The substances listed here aremainly ones that have an electron mobility of 10⁻⁶ cm²/Vs or higher.Note that any substance other than the substances listed here may beused for the electron-transport layer 107 as long as theelectron-transport property is higher than the hole-transport property.

The electron-transport layer 107 is not limited to a single layer, butmay be a stack of two or more layers each containing any of thesubstances listed above.

The electron-injection layer 108 is a layer containing a substance witha high electron-injection property. For the electron-injection layer108, an alkali metal, an alkaline earth metal, or a compound thereof,such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride(CaF₂), or lithium oxide (LiO_(x)) can be used. A rare earth metalcompound such as erbium fluoride (ErF₃) can also be used. An electridemay also be used for the electron-injection layer 108. Examples of theelectride include a substance in which electrons are added at highconcentration to calcium oxide-aluminum oxide. Any of the substances forforming the electron-transport layer 107, which are given above, can beused.

A composite material in which an organic compound and an electron donor(donor) are mixed may also be used for the electron-injection layer 108.Such a composite material is excellent in an electron-injection propertyand an electron-transport property because electrons are generated inthe organic compound by the electron donor. In this case, the organiccompound is preferably a material that is excellent in transporting thegenerated electrons. Specifically, for example, the substances forforming the electron-transport layer 107 (e.g., a metal complex and aheteroaromatic compound), which are given above, can be used. As theelectron donor, a substance showing an electron-donating property withrespect to the organic compound may be used. Specifically, an alkalimetal, an alkaline earth metal, and a rare earth metal are preferable,and lithium, cesium, magnesium, calcium, erbium, ytterbium, and the likecan be given. In addition, an alkali metal oxide and an alkaline earthmetal oxide are preferable, and lithium oxide, calcium oxide, and bariumoxide are given. A Lewis base such as magnesium oxide can also be used.An organic compound such as tetrathiafulvalene (abbreviation: TTF) canalso be used.

Note that each of the above-described hole-injection layer 104,hole-transport layer 105, light-emitting layer 106, electron-transportlayer 107, and electron-injection layer 108 can be formed by a methodsuch as an evaporation method (e.g., a vacuum evaporation method), anink-jet method, or a coating method.

In the above-described light-emitting element, current flows because ofa potential difference generated between the first electrode 101 and thesecond electrode 102 and holes and electrons are recombined in the ELlayer 103, whereby light is emitted. Then, the emitted light isextracted outside through one or both of the first electrode 101 and thesecond electrode 102. Thus, one or both of the first electrode 101 andthe second electrode 102 are electrodes having light-transmittingproperties.

By forming the light-emitting element having the structure described inthis embodiment as described above, even when the light-emitting area isshifted due to a change in the carrier balance over driving time,another light-emitting layer can compensate for the change, and thestable state of the whole light-emitting layer can be kept. Thus, thelight-emitting element can keep favorable characteristics afterlong-time driving.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 2

In this embodiment, as one embodiment of the present invention, alight-emitting element (hereinafter referred to as tandem light-emittingelement) in which a charge-generation layer is provided between aplurality of EL layers is described with reference to FIGS. 2A and 2B.

A light-emitting element described in this embodiment is a tandemlight-emitting element including a plurality of EL layers (a first ELlayer 202(1) and a second EL layer 202(2)) between a pair of electrodes(a first electrode 201 and a second electrode 204) as illustrated inFIG. 2A.

In this embodiment, the first electrode 201 functions as an anode, andthe second electrode 204 functions as a cathode. Note that the firstelectrode 201 and the second electrode 204 can have structures similarto those described in Embodiment 1. In addition, all or any of theplurality of EL layers (the first EL layer 202(1) and the second ELlayer 202(2)) may have structures similar to those described inEmbodiment 1. In other words, the structures of the first EL layer202(1) and the second EL layer 202(2) may be the same or different fromeach other and can be similar to those of the EL layers described inEmbodiment 1.

In addition, a charge-generation layer 205 is provided between theplurality of EL layers (the first EL layer 202(1) and the second ELlayer 202(2)). The charge-generation layer 205 has a function ofinjecting electrons into one of the EL layers and injecting holes intothe other of the EL layers when voltage is applied between the firstelectrode 201 and the second electrode 204. In this embodiment, whenvoltage is applied such that the potential of the first electrode 201 ishigher than that of the second electrode 204, the charge-generationlayer 205 injects electrons into the first EL layer 202(1) and injectsholes into the second EL layer 202(2).

Note that in terms of light extraction efficiency, the charge-generationlayer 205 preferably has a property of transmitting visible light(specifically, the charge-generation layer (I) 205 has a visible lighttransmittance of 40% or more). The charge-generation layer 205 functionseven when it has lower conductivity than the first electrode 201 or thesecond electrode 204.

The charge-generation layer 205 may have either a structure in which anelectron acceptor (acceptor) is added to a hole-transport material or astructure in which an electron donor (donor) is added to anelectron-transport material. Alternatively, both of these structures maybe stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, as theorganic compound having a high hole-transport property, for example, anaromatic amine compound such as NPB, TPD, TDATA, MTDATA, or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), or the like can be used. The substances listedhere are mainly ones that have a hole mobility of 10⁻⁶ cm²/Vs or higher.Note that any organic compound other than the compounds listed here maybe used as long as the hole-transport property is higher than theelectron-transport property.

As the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. Transition metal oxidescan also be given. Oxides of metals belonging to Groups 4 to 8 of theperiodic table can also be given. Specifically, vanadium oxide, niobiumoxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, and rhenium oxide are preferable because of their highelectron-accepting properties. Among these, molybdenum oxide isespecially preferable since it is stable in the air, has a lowhygroscopic property, and is easy to handle.

On the other hand, in the case of the structure in which an electrondonor is added to an electron-transport material, as theelectron-transport material, for example, a metal complex having aquinoline skeleton or a benzoquinoline skeleton, such as Alq, Almq₃,BeBq₂, or BAlq, or the like can be used. Alternatively, a metal complexhaving an oxazole-based ligand or a thiazole-based ligand, such asZn(BOX)₂ or Zn(BTZ)₂ can be used. Alternatively, in addition to such ametal complex, PBD, OXD-7, TAZ, Bphen, BCP, or the like can be used. Thesubstances listed here are mainly ones that have an electron mobility of10⁻⁶ cm²/Vs or higher. Note that any organic compound other than thecompounds listed here may be used as long as the electron-transportproperty is higher than the hole-transport property.

As the electron donor, it is possible to use an alkali metal, analkaline earth metal, a rare earth metal, metals belonging to Groups 2and 13 of the periodic table, or an oxide or carbonate thereof.Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or thelike is preferably used. Alternatively, an organic compound such astetrathianaphthacene may be used as the electron donor.

Note that forming the charge-generation layer 205 by using any of theabove materials can suppress a drive voltage increase caused by thestack of the EL layers.

Although the light-emitting element including two EL layers is describedin this embodiment, the present invention can be similarly applied to alight-emitting element in which 11 EL layers (202(1) to 202(n)) (n isthree or more) are stacked as illustrated in FIG. 2B. In the case wherea plurality of EL layers are included between a pair of electrodes as inthe light-emitting element according to this embodiment, by providingcharge-generation layers (205(1) to 205(n−1)) between the EL layers,light emission in a high luminance region can be obtained with currentdensity kept low. Since the current density can be kept low, the elementcan have a long lifetime. When the light-emitting element is applied tolighting, voltage drop due to resistance of an electrode material can bereduced, which results in homogeneous light emission in a large area. Inaddition, a low-power-consumption light-emitting device that can bedriven at low voltage can be obtained.

When the EL layers have different emission colors, a desired emissioncolor can be obtained from the whole light-emitting element. Forexample, in the light-emitting element having two EL layers, when anemission color of the first EL layer and an emission color of the secondEL layer are made to be complementary colors, a light-emitting elementemitting white light as a whole light-emitting element can also beobtained. Note that “complementary colors” refer to colors that canproduce an achromatic color when mixed. In other words, emission ofwhite light can be obtained by mixture of light emitted from substanceswhose emission colors are complementary colors.

The same can be applied to a light-emitting element having three ELlayers. For example, the light-emitting element as a whole can providewhite light emission when the emission color of the first EL layer isred, the emission color of the second EL layer is green, and theemission color of the third EL layer is blue.

As a light-emitting device including the above-described light-emittingelement, a passive matrix light-emitting device and an active matrixlight-emitting device can be fabricated. It is also possible tofabricate a light-emitting device having a microcavity structure. Eachof the light-emitting devices is one embodiment of the presentinvention.

Note that there is no particular limitation on the structure of thetransistor (FET) in the case of fabricating the active matrixlight-emitting device. For example, a staggered FET or an invertedstaggered FET can be used as appropriate. A driver circuit formed over aFET substrate may be formed of both an n-type FET and a p-type FET oronly either an n-type FET or a p-type FET. Furthermore, there is noparticular limitation on the crystallinity of a semiconductor film usedfor the FET. For example, either an amorphous semiconductor film or acrystalline semiconductor film can be used. Examples of a semiconductormaterial include Group IV semiconductors (e.g., silicon), Group IIIsemiconductors (e.g., gallium), compound semiconductors (including oxidesemiconductors), and organic semiconductors.

Note that the structure described in this embodiment can be used inappropriate combination with the structure described in any of the otherembodiments.

Embodiment 3

In this embodiment, a light-emitting device which is one embodiment ofthe present invention will be described.

A light-emitting device described in this embodiment has a micro opticalresonator (microcavity) structure in which a light resonant effectbetween a pair of electrodes is utilized. The light-emitting deviceincludes a plurality of light-emitting elements each of which has atleast an EL layer 305 between a pair of electrodes (a reflectiveelectrode 301 and a transflective electrode 302) as illustrated in FIG.3. The EL layer 305 includes at least a light-emitting layer 304 servingas a light-emitting area and may further include a hole-injection layer,a hole-transport layer, an electron-transport layer, anelectron-injection layer, a charge-generation layer, and the like.

In this embodiment, a light-emitting device is described which includestwo kinds of light-emitting elements (a first light-emitting element310R and a second light-emitting element 310G) as illustrated in FIG. 3.

The first light-emitting element 310R and the second light-emittingelement 310G each have a structure in which a transparent conductivelayer 303, the EL layer 305 partly including the light-emitting layer304, and the transflective electrode 302 are stacked in this order overthe reflective electrode 301.

The reflective electrode 301, the EL layer 305, and the transflectiveelectrode 302 are common to the two kinds of light-emitting elements inthis embodiment. The light-emitting layer 304 has a stacked-layerstructure of a layer that emits light (λ_(G)) having a peak in a firstwavelength region and a layer that emits light (λ_(R)) having a peak ina second wavelength region. In this case, the above wavelengths satisfythe relation of λ_(G)<λ_(R).

Each of the light-emitting elements described in this embodiment has astructure in which the EL layer 305 is provided between the reflectiveelectrode 301 and the transflective electrode 302. Light emitted in alldirections from the light-emitting layers included in the EL layer 305is resonated by the reflective electrode 301 and the transflectiveelectrode 302 which function as a micro optical resonator (amicrocavity).

Note that the reflective electrode 301 is formed using a conductivematerial having reflectivity, and a film whose visible lightreflectivity is 40% to 100%, preferably 70% to 100%, and whoseresistivity is 1×10⁻² Ωcm or lower is used. In addition, thetransflective electrode 302 is formed using a conductive material havingreflectivity and a conductive material having a light-transmittingproperty, and a film whose visible light reflectivity is 20% to 80%,preferably 40% to 70%, and whose resistivity is 1×10⁻² Ωcm or lower isused.

The transparent conductive layers 303 of the light-emitting element 310Rand 310G are formed so that the thicknesses thereof are different,whereby the two kinds of light-emitting elements differ from each otherin the optical distance between the reflective electrode 301 and thetransflective electrode 302. Thus, light with a wavelength that isresonated between the reflective electrode 301 and the transflectiveelectrode 302 can be intensified while light with a wavelength that isnot resonated therebetween can be attenuated, so that light withwavelengths which differ depending on the light-emitting elements can beextracted.

Furthermore, in the first light-emitting element 310R, the totalthickness (total optical thickness) of components from the reflectiveelectrode 301 to the transflective electrode 302 is set to mλ_(R)/2 (mis a natural number), and in the second light-emitting element 310G, thetotal thickness of components from the reflective electrode 301 to thetransflective electrode 302 is set to mλ_(G)/2 (m is a natural number).

In this manner, the light (λ_(R)) emitted from the second light-emittinglayer 304R included in the EL layer 305 is mainly extracted from thefirst light-emitting element 310R, and the light (λ_(G)) emitted fromthe first light-emitting layer 304G included in the EL layer 305 ismainly extracted from the second light-emitting element 310G. Note thatthe light extracted from each of the light-emitting elements is emittedfrom the transflective electrode 302 side.

Furthermore, strictly speaking, the total thickness from the reflectiveelectrode 301 to the transflective electrode 302 can be the totalthickness from a reflection region in the reflective electrode 301 to areflection region in the transflective electrode 302. However, it isdifficult to precisely determine the positions of the reflection regionsin the reflective electrode 301 and the transflective electrode 302;therefore, it is presumed that the above effect can be sufficientlyobtained wherever the reflection regions may be set in the reflectiveelectrode 301 and the transflective electrode 302.

Moreover, in the first light-emitting element 310R, the optical distancebetween the reflective electrode 301 and the second light-emitting layer304R is adjusted to a desired thickness ((2m′+1)λ_(R)/4, where m′ is anatural number); thus, light emitted from the second light-emittinglayer 304R can be amplified.

Note that strictly speaking, the optical distance between the reflectiveelectrode 301 and the second light-emitting layer 304R can be theoptical distance between a reflection region in the reflective electrode301 and a light-emitting region in the second light-emitting layer 304R.However, it is difficult to precisely determine the positions of thereflection region in the reflective electrode 301 and the light-emittingregion in the second light-emitting layer 304R; therefore, it ispresumed that the above effect can be sufficiently obtained wherever thelight-emitting region may be set in the second light-emitting layer304R.

Moreover, in the second light-emitting element 310G, the opticaldistance between the reflective electrode 301 and the firstlight-emitting layer 304G is adjusted to a desired thickness((2m″+1)λ_(G)/4, where m″ is a natural number); thus, light emitted fromthe first light-emitting layer 304G can be amplified.

Note that strictly speaking, the optical distance between the reflectiveelectrode 301 and the first light-emitting layer 304G can be the opticaldistance between a reflection region in the reflective electrode 301 anda light-emitting region in the first light-emitting layer 304G. However,it is difficult to precisely determine the positions of the reflectionregion in the reflective electrode 301 and the light-emitting region inthe first light-emitting layer 304G; therefore, it is presumed that theabove effect can be sufficiently obtained wherever the reflection regionand the light-emitting region may be set in the reflective electrode 301and the first light-emitting layer 304G, respectively.

The optical distance between the reflective electrode 301 and thelight-emitting layer 304 is set as described above. However, in the casewhere the light-emitting layer has such a stacked-layer structure(specifically, the light-emitting layer includes a plurality of layersthat emit light (λ_(G)) having a peak in the same wavelength region) asis described in Embodiment 1, the optical distance between thereflective electrode 301 and the light-emitting layer 304 corresponds tothe optical distance between the reflective electrode 301 and one of thelight-emitting layers that emit light (λ_(G)) having a peak in the samewavelength region.

Note that although each of the light-emitting elements in theabove-described structure includes a plurality of light-emitting layersin the EL layer, the present invention is not limited thereto; forexample, the structure of the tandem light-emitting element which isdescribed in Embodiment 2 can be combined, in which case a plurality ofEL layers and a charge generation layer interposed therebetween areprovided in one light-emitting element and one or more light-emittinglayers are formed in each of the EL layers.

The light-emitting device described in this embodiment has a microcavitystructure, in which light with wavelengths which differ depending on thelight-emitting elements can be extracted even when they include the sameEL layers, so that it is not needed to form light-emitting elements forthe colors of R, G, and B. Therefore, the above structure isadvantageous for full color display owing to easiness in achievinghigher resolution display or the like. Note that a combination withcoloring layers (color filters) is also possible. In addition, emissionintensity with a predetermined wavelength in the front direction can beincreased, whereby power consumption can be reduced. The above structureis particularly useful in the case of being applied to a color display(image display device) including pixels of three or more colors but mayalso be applied to lighting or the like.

Embodiment 4

In this embodiment, a light-emitting device including a light-emittingelement which is one embodiment of the present invention will bedescribed.

The light-emitting device may be either a passive matrix typelight-emitting device or an active matrix type light-emitting device.Note that any of the light-emitting elements described in the otherembodiments can be used for the light-emitting device described in thisembodiment.

In this embodiment, an active matrix light-emitting device is describedwith reference to FIGS. 4A and 4B.

Note that FIG. 4A is a top view illustrating a light-emitting device andFIG. 4B is a cross-sectional view taken along the chain line A-A′ inFIG. 4A. The active matrix light-emitting device according to thisembodiment includes a pixel portion 402 provided over an elementsubstrate 401, a driver circuit portion (a source line driver circuit)403, and driver circuit portions (gate line driver circuits) 404 a and404 b. The pixel portion 402, the driver circuit portion 403, and thedriver circuit portions 404 a and 404 b are sealed between the elementsubstrate 401 and a sealing substrate 406 with a sealant 405.

In addition, over the element substrate 401, a lead wiring 407 forconnecting an external input terminal, through which a signal (e.g., avideo signal, a clock signal, a start signal, a reset signal, or thelike) or electric potential from the outside is transmitted to thedriver circuit portion 403 and the driver circuit portions 404 a and 404b, is provided. Here, an example is described in which a flexibleprinted circuit (FPC) 408 is provided as the external input terminal.Although only the FPC is illustrated here, the FPC may be provided witha printed wiring board (PWB). The light-emitting device in thisspecification includes, in its category, not only the light-emittingdevice itself but also the light-emitting device provided with the FPCor the PWB.

Next, a cross-sectional structure is described with reference to FIG.4B. The driver circuit portion and the pixel portion are formed over theelement substrate 401; the driver circuit portion 403 that is the sourceline driver circuit and the pixel portion 402 are illustrated here.

The driver circuit portion 403 is an example in which an FET 409 and anFET 410 are combined. Note that each of the FET 409 and the FET 410included in the driver circuit portion 403 may be formed with a circuitincluding transistors having the same conductivity type (either ann-channel transistor or a p-channel transistor) or a CMOS circuitincluding an n-channel transistor and a p-channel transistor. Althoughthis embodiment shows a driver integrated type in which the drivercircuit is formed over the substrate, the driver circuit is notnecessarily formed over the substrate, and may be formed outside thesubstrate.

The pixel portion 402 includes a plurality of pixels each of whichincludes a switching FET 411, a current control FET 412, and a firstelectrode (anode) 413 that is electrically connected to a wiring (asource electrode or a drain electrode) of the current control FET 412.Although the pixel portion 402 includes two FETs, the switching FET 411and the current control FET 412, in this embodiment, one embodiment ofthe present invention is not limited thereto. The pixel portion 402 mayinclude, for example, three or more FETs and a capacitor in combination.

As the FETs 409, 410, 411, and 412, for example, a staggered transistoror an inverted staggered transistor can be used. Examples of asemiconductor material that can be used for the FETs 409, 410, 411, and412 include Group IV semiconductors (e.g., silicon), Group IIIsemiconductors (e.g., gallium), compound semiconductors, oxidesemiconductors, and organic semiconductors. In addition, there is noparticular limitation on the crystallinity of the semiconductormaterial, and an amorphous semiconductor or a crystalline semiconductorcan be used. In particular, an oxide semiconductor is preferably usedfor the FETs 409, 410, 411, and 412. Examples of the oxide semiconductorinclude an In—Ga oxide and an In-M-Zn oxide (M is Al, Ga, Y, Zr, La, Ce,or Nd). For example, an oxide semiconductor material that has an energygap of 2 eV or more, preferably 2.5 eV or more, further preferably 3 eVor more is used for the FETs 409, 410, 411, and 412, so that theoff-state current of the transistors can be reduced.

In addition, an insulator 414 is formed to cover end portions of thefirst electrode (anode) 413. In this embodiment, the insulator 414 isformed using a positive photosensitive acrylic resin. The firstelectrode 413 is used as an anode in this embodiment.

The insulator 414 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof. This enables thecoverage with a film to be formed over the insulator 414 to befavorable. The insulator 414 can be formed using, for example, either anegative photosensitive resin or a positive photosensitive resin.

The material of the insulator 414 is not limited to an organic compoundand an inorganic compound such as silicon oxide, silicon oxynitride, orsilicon nitride can also be used.

An EL layer 415 and a second electrode (cathode) 416 are stacked overthe first electrode (anode) 413. In the EL layer 415, at least alight-emitting layer is provided, and the light-emitting layer has thestacked structure described in Embodiment 1. In addition to thelight-emitting layer, a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, acharge-generation layer, and the like can be provided as appropriate inthe EL layer 415.

A light-emitting element 417 is formed of a stack of the first electrode(anode) 413, the EL layer 415, and the second electrode (cathode) 416.For the first electrode (anode) 413, the EL layer 415, and the secondelectrode (cathode) 416, any of the materials given in Embodiment 1 canbe used. Although not illustrated, the second electrode (cathode) 416 iselectrically connected to the FPC 408 which is an external inputterminal.

Although the cross-sectional view of FIG. 4B illustrates only onelight-emitting element 417, a plurality of light-emitting elements arearranged in matrix in the pixel portion 402. Light-emitting elementsthat emit light of three kinds of colors (R, G, and B) are selectivelyformed in the pixel portion 402, whereby a light-emitting device capableof full color display can be obtained. In addition to the light-emittingelements that emit light of three kinds of colors (R, G, and B), forexample, light-emitting elements that emit light of white (W), yellow(Y), magenta (M), cyan (C), and the like may be formed. For example, thelight-emitting elements that emit light of a plurality of kinds ofcolors are used in combination with the light-emitting elements thatemit light of three kinds of colors (R, G, and B), whereby effects suchas an improvement in color purity and a reduction in power consumptioncan be obtained. Alternatively, a light-emitting device that is capableof full color display may be fabricated by combination with colorfilters.

Furthermore, the sealing substrate 406 is attached to the elementsubstrate 401 with the sealant 405, whereby a light-emitting element 417is provided in a space 418 surrounded by the element substrate 401, thesealing substrate 406, and the sealant 405. Note that the space 418 maybe filled with an inert gas (such as nitrogen and argon) or the sealant405.

An epoxy-based resin or glass fit is preferably used for the sealant405. The material preferably allows as little moisture and oxygen aspossible to penetrate. As the sealing substrate 406, a glass substrate,a quartz substrate, or a plastic substrate formed of fiber-reinforcedplastic (FRP), polyvinyl fluoride) (PVF), polyester, acrylic, or thelike can be used. In the case where glass frit is used as the sealant,the element substrate 401 and the sealing substrate 406 are preferablyglass substrates for high adhesion

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be used inappropriate combination with the structure described in any of the otherembodiments.

Embodiment 5

In this embodiment, examples of a variety of electronic devices whichare completed using a light-emitting device are described with referenceto FIGS. 5A to 5D. The light-emitting device is fabricated using thelight-emitting element of one embodiment of the present invention.

Examples of electronic appliances including the light-emitting deviceinclude television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as portable telephone devices), portable gamemachines, portable information terminals, audio playback devices, andlarge game machines such as pachinko machines. Specific examples of theelectronic appliances are illustrated in FIGS. 5A to 5D.

FIG. 5A illustrates an example of a television device. In the televisiondevice 7100, a display portion 7103 is incorporated in a housing 7101.Images can be displayed by the display portion 7103, and thelight-emitting device can be used for the display portion 7103. Inaddition, here, the housing 7101 is supported by a stand 7105.

The television device 7100 can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasts can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 5B illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer can be manufactured using the light-emitting device forthe display portion 7203.

FIG. 5C illustrates a smart watch, which includes a housing 7302, adisplay panel 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like.

The display panel 7304 mounted in the housing 7302 serving as a bezelincludes a non-rectangular display region. The display panel 7304 candisplay an icon 7305 indicating time, another icon 7306, and the like.

The smart watch illustrated in FIG. 5C can have a variety of functions,for example, a function of displaying a variety of information (e.g., astill image, a moving image, and a text image) on a display portion, atouch panel function, a function of displaying a calendar, date, time,and the like, a function of controlling processing with a variety ofsoftware (programs), a wireless communication function, a function ofbeing connected to a variety of computer networks with a wirelesscommunication function, a function of transmitting and receiving avariety of data with a wireless communication function, and a functionof reading program or data stored in a recording medium and displayingthe program or data on a display portion.

The housing 7302 can include a speaker, a sensor (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone, and the like. Note that the smart watch can be manufacturedusing the light-emitting device for the display panel 7304.

FIG. 5D illustrates an example of a mobile phone. A mobile phone 7400includes a housing 7401 provided with a display portion 7402, amicrophone 7406, a speaker 7405, a camera 7407, an external connectionportion 7404, an operation button 7403, and the like. In the case wherethe light-emitting element of one embodiment of the present invention isformed over a flexible substrate, the light-emitting element can be usedfor the display portion 7402 having a curved surface as illustrated inFIG. 5D.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 5D is touched with a finger or the like, data can be input to themobile phone 7400. In addition, operations such as making a call andcomposing an e-mail can be performed by touch on the display portion7402 with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting data such as characters. Thethird mode is a display-and-input mode in which two modes of the displaymode and the input mode are combined.

For example, in the case of making a call or creating e-mail, acharacter input mode mainly for inputting characters is selected for thedisplay portion 7402 so that characters displayed on the screen can beinput. In this case, it is preferable to display a keyboard or numberbuttons on almost the entire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone 7400, display on the screen of the display portion 7402 canbe automatically changed by determining the orientation of the mobilephone 7400 (whether the mobile phone is placed horizontally orvertically for a landscape mode or a portrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401. The screenmodes can be switched depending on the kind of images displayed on thedisplay portion 7402. For example, when a signal of an image displayedon the display portion is a signal of moving image data, the screen modeis switched to the display mode. When the signal is a signal of textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. In addition, when a backlightor a sensing light source that emits near-infrared light is provided inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

As described above, the electronic appliances can be obtained using thelight-emitting device that includes the light-emitting element of oneembodiment of the present invention. Note that the light-emitting devicecan be used for electronic appliances in a variety of fields withoutbeing limited to the electronic appliances described in this embodiment.

Note that the structure described in this embodiment can be used inappropriate combination with the structure described in any of the otherembodiments.

Embodiment 6

In this embodiment, examples of lighting devices which are completedusing a light-emitting device are described with reference to FIG. 6.The light-emitting device is fabricated using a light-emitting elementof one embodiment of the present invention.

FIG. 6 illustrates an example in which the light-emitting device is usedas an indoor lighting device 8001. Since the light-emitting device canhave a large area, it can be used for a lighting device having a largearea. In addition, a lighting device 8002 in which a light-emittingregion has a curved surface can also be obtained with the use of ahousing with a curved surface. A light-emitting element included in thelight-emitting device described in this embodiment is in a thin filmform, which allows the housing to be designed more freely. Thus, thelighting device can be elaborately designed in a variety of ways. Inaddition, a wall of the room may be provided with a large-sized lightingdevice 8003.

When the light-emitting device is used for a table by being used as asurface of a table, a lighting device 8004 that has a function as atable can be obtained. When the light-emitting device is used as part ofother furniture, a lighting device that functions as the furniture canbe obtained.

As described above, a variety of lighting devices that include thelight-emitting device can be obtained. Note that these lighting devicesare also embodiments of the present invention.

Note that the structure described in this embodiment can be used inappropriate combination with the structure described in any of the otherembodiments.

Example 1

In this example, Light-emitting Element 1 of one embodiment of thepresent invention and Comparative Light-emitting Element 2 werefabricated. The element structures of Light-emitting Element 1 andComparative Light-emitting Element 2 are described in detail withreference to FIG. 7A and FIG. 7B, respectively. Note that the commonreference numerals are collectively described. Chemical formulae ofmaterials used in this example are shown below.

<<Fabrication of Light-Emitting Element 1 and Comparative Light-EmittingElement 2>>

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 700 by a sputtering method, so that a firstelectrode 701, which functions as an anode, was formed. The thicknesswas 110 nm and the electrode area was 2 mm×2 mm.

Then, as pretreatment for forming Light-emitting Element 1 andComparative Light-emitting Element 2 over the substrate 700, UV ozonetreatment was performed for 370 seconds after washing of a surface ofthe substrate with water and baking that was performed at 200° C. for 1hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 60 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 700 was cooled down for about 30 minutes.

Next, the substrate 700 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 700 over whichthe first electrode 701 was formed faced downward. In this example, acase will be described in which a hole-injection layer 704, ahole-transport layer 705, a light-emitting layer 706, anelectron-transport layer 707, and an electron-injection layer 708, whichare included in an EL layer 703, are sequentially formed by a vacuumevaporation method.

After reducing the pressure in the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)-benzene (abbreviation: DBT3P-II) andmolybdenum oxide were co-evaporated at a mass ratio of 1:0.5 (DBT3P-II(abbreviation):molybdenum oxide), whereby the hole-injection layer 704was formed over the first electrode 701. The thickness of thehole-injection layer 704 was 33 nm. Note that the co-evaporation is anevaporation method in which some different substances are evaporatedfrom some different evaporation sources at the same time.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation to a thickness of 20 nm, so thatthe hole-transport layer 705 was formed.

Next, the light-emitting layer 706 was formed over the hole-transportlayer 705.

In the case of Light-emitting Element 1, the light-emitting layer 706has a stacked-layer structure of three layers of a first light-emittinglayer 706 a, a second light-emitting layer 706 b, and a thirdlight-emitting layer 706 c as illustrated in FIG. 7A.

The first light-emitting layer 706 a was formed to have a thickness of20 nm by co-evaporating2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF), and(Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) at a mass ratio of 0.8:0.2:0.06(2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]).

The second light-emitting layer 706 b was formed to have a thickness of10 nm by co-evaporating 2mDBTBPDBq-II (abbreviation), PCBBiF(abbreviation), and bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-dmp)₂(acac)]) at a mass ratio of 0.9:0.1:0.06(2mDBTBPDBq-II:PCBBiF:[Ir(dmdppr-dmp)₂(acac)]).

The third light-emitting layer 706 c was formed to have a thickness of10 nm by co-evaporating 2mDBTBPDBq-II (abbreviation), PCBBiF(abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) at a mass ratioof 0.8:0.2:0.06 (2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]).

In the case of Comparative Light-emitting Element 2, the light-emittinglayer 706 has a stacked-layer structure of two layers of a firstlight-emitting layer 706 a′ and a second light-emitting layer 706 b′ asillustrated in FIG. 7B.

The first light-emitting layer 706 a′ was formed to have a thickness of20 nm by co-evaporating 2mDBTBPDBq-II (abbreviation), PCBBiF(abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) at a mass ratioof 0.8:0.2:0.06 (2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]).

The second light-emitting layer 706 b′ was formed to have a thickness of20 nm by co-evaporating 2mDBTBPDBq-II (abbreviation) and[Ir(dmdppr-dmp)₂(acac)] (abbreviation) at a mass ratio of 1:0.06(2mDBTBPDBq-II:[Ir(dmdppr-dmp)₂(acac)]).

Next, the electron-transport layer 707 was formed over thelight-emitting layer 706.

In the case of Light-emitting Element 1, 2mDBTBPDBq-II (abbreviation)was deposited by evaporation to a thickness of 30 nm and thenbathophenanthroline (abbreviation: Bphen) was deposited by evaporationto a thickness of 15 nm, whereby the electron-transport layer 707 wasformed.

In the case of Comparative Light-emitting Element 2, 2mDBTBPDBq-II(abbreviation) was deposited by evaporation to a thickness of 35 nm andthen bathophenanthroline (abbreviation: Bphen) was deposited byevaporation to a thickness of 15 nm, whereby the electron-transportlayer 707 was formed.

Next, lithium fluoride was deposited by evaporation to a thickness of 1nm, whereby the electron-injection layer 708 was formed over theelectron-transport layer 707.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmover the electron-injection layer 708 to form a second electrode 702serving as a cathode; thus, Light-emitting Element 1 and ComparativeLight-emitting Element 2 were obtained. Note that in all the aboveevaporation steps, evaporation was performed by a resistance-heatingmethod.

Element structures of Light-emitting Element 1 and ComparativeLight-emitting Element 2 obtained as described above are shown in Table1.

TABLE 1 Electron- First Hole-injection Hole-transport injection Secondelectrode layer layer Light-emitting layer Electron-transport layerlayer electrode Light- ITSO DBT3P-II:MoOx BPAFLP * ** *** 2mDBTBPDBq-IIBphen LiF Al emitting (110 nm) (1:0.5 33 nm) (20 nm) (30 nm) (15 nm) (1nm) (200 nm) Element 1 Comparative * **** 2mDBTBPDBq-II Light- (35 nm)emitting Element 2 * 2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)](0.8:0.2:0.06 20 nm) ** 2mDBTBPDBq-II:PCBBiF:[Ir(dmdppr-dmp)₂(acac)](0.9:0.1:0.06 10 nm) *** 2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)](0.8:0.2:0.06 10 nm) **** 2mDBTBPDBq-II:[Ir(dmdppr-dmp)₂(acac)] (1:0.0620 nm)

Furthermore, each of the fabricated Light-emitting Element 1 andComparative Light-emitting Element 2 was sealed in a glove boxcontaining a nitrogen atmosphere so as not to be exposed to the air(specifically, a sealant was applied onto an outer edge of the element,and the sealant was irradiated with ultraviolet light with a wavelengthof 365 nm at 6 J/cm² and heat treatment was performed at 80° C. for 1hour at the time of sealing).

<<Operation Characteristics of Light-Emitting Element 1 and ComparativeLight-Emitting Element 2>>

Operation characteristics of Light-emitting Element 1 and ComparativeLight-emitting Element 2 were measured. Note that the measurement wascarried out at room temperature (under an atmosphere in which thetemperature was kept at 25° C.).

FIG. 8 shows luminance-current efficiency characteristics ofLight-emitting Element 1 and Comparative Light-emitting Element 2. InFIG. 8, the vertical axis represents current efficiency (cd/A) and thehorizontal axis represents luminance (cd/m²). Furthermore, FIG. 9 showsluminance-external quantum efficiency characteristics of Light-emittingElement 1 and Comparative Light-emitting Element 2. In FIG. 9, thevertical axis represents external quantum efficiency (%) and thehorizontal axis represents luminance (cd/m²). In addition, FIG. 10 showsvoltage-luminance characteristics of Light-emitting Element 1 andComparative Light-emitting Element 2. In FIG. 10, the vertical axisrepresents luminance (cd/m²) and the horizontal axis represents voltage(V).

Table 2 shows initial values of main characteristics of Light-emittingElement 1 and Comparative Light-emitting Element 2 at a luminance ofapproximately 1000 cd/m².

TABLE 2 External Current Current Power quantum Voltage Current densityChromaticity Luminance efficiency efficiency efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 3.2 0.06 1.5 (0.49,0.51) 1000 68 67 25 emitting Element 1 Comparative 3.4 0.062 1.5 (0.48,0.51) 970 62 59 23 Light- emitting Element 2

From the above results, it is found that Light-emitting Element 1 andComparative Light-emitting Element 2, which were fabricated in thisexample, both have high external quantum efficiency; however,Light-emitting Element 1 having the element structure of one embodimentof the present invention has higher current efficiency than ComparativeLight-emitting Element 2.

FIG. 11 shows emission spectra in the initial stage of driving when acurrent with a current density of 2.5 mA/cm² was supplied toLight-emitting Element 1 and Comparative Light-emitting Element 2. Asshown in FIG. 11, the emission spectra of Light-emitting Element 1 andComparative Light-emitting Element 2 both have peaks at approximately548 nm and approximately 615 nm, which indicates that the peaks areattributed to light emission from [Ir(dmdppr-dmp)₂(acac)] and[Ir(tBuppm)₂(acac)], which are phosphorescent organometallic iridiumcomplexes. However, it is also found that the peak at approximately 615nm in the initial stage of driving of Comparative Light-emitting Element2 is weaker than that of Light-emitting Element 1.

FIG. 12 shows results of reliability tests of Light-emitting Element 1and Comparative Light-emitting Element 2. In FIG. 12, the vertical axisrepresents normalized luminance (%) when an initial luminance is 100%and the horizontal axis represents driving time (h) of the element. Notethat in the reliability tests, Light-emitting Element 1 and ComparativeLight-emitting Element 2 were driven under the conditions where theinitial luminance was set to 5000 cd/m² and the current density wasconstant. As a result, it is found that Light-emitting Element 1 has alonger lifetime than Comparative Light-emitting Element 2.

Furthermore, changes in emission spectra by the above reliability testswere measured. FIG. 13A and FIG. 13B show a measurement result ofLight-emitting Element 1 and a measurement result of ComparativeLight-emitting Element 2, respectively. Note that a result before thereliability test is obtained by performing measurement at the time ofstarting the reliability test, and a result after the reliability testis obtained by performing measurement after the reliability test for1000 hours under the conditions where the initial luminance was set to5000 cd/m² and the current density was constant.

From the results of FIGS. 13A and 13B, it is found that inLight-emitting Element 1, the amount of change in the whole emissionspectrum before and after the reliability test, which is the sum of adecrease in the peak at approximately 548 nm and an increase in the peakat approximately 615 nm, is smaller than that in ComparativeLight-emitting Element 2. This indicates that in Light-emitting Element1 having the element structure of one embodiment of the presentinvention, the peak intensity of light emission is not easily changedeven after long-time driving.

Note that the combination of 2mDBTBPDBq-II (abbreviation) and PCBBiF(abbreviation), which are used for the light-emitting layer in thisexample, forms an exciplex.

Example 2

In this example, as light-emitting elements of one embodiment of thepresent invention and comparative light-emitting elements,Light-emitting Element 3, Comparative Light-emitting Element 4,Light-emitting Element 5, and Comparative Light-emitting Element 6 werefabricated. Note that the details are described with reference to FIGS.14A and 14B. A light-emitting element in this example has a combinationstructure of the tandem type structure described in Embodiment 2 and themicrocavity structure described in Embodiment 3. Chemical formulae ofmaterials used in this example are shown below.

<<Fabrication of Light-Emitting Element 3, Comparative Light-EmittingElement 4, Light-Emitting Element 5, and Comparative Light-EmittingElement 6>>

As light-emitting elements in this example, Light-emitting Element 3 and

Comparative Light-emitting Element 4 are shown on the left side of FIG.14A and the right side of FIG. 14A, respectively, and Light-emittingElement 3 and Comparative Light-emitting Element 4 both emit greenlight. Furthermore, Light-emitting Element 5 and ComparativeLight-emitting Element 6 are shown on the left side of FIG. 14B and theright side of FIG. 14B, respectively, and Light-emitting Element 5 andComparative Light-emitting Element 6 both emit red light. Note that ineach of the light-emitting elements, light is emitted from the secondelectrode 4003 side.

Light-emitting Element 3 and Comparative Light-emitting Element 4 inFIG. 14A are different from each other in only a structure of alight-emitting layer (4013 b,4013 b′) in a second EL layer 4002 b.Light-emitting Element 5 and Comparative Light-emitting Element 6 inFIG. 14B are also different from each other in only a structure of alight-emitting layer (4013 b, 4013 b′) in the second EL layer 4002 b.Furthermore, Light-emitting Element 3 and Comparative Light-emittingElement 4 in FIG. 14A are optically adjusted to emit green light andLight-emitting Element 5 and Comparative Light-emitting Element 6 inFIG. 14B are optically adjusted to emit red light; thus, a firstelectrode 4101 in FIG. 14B and a first electrode 4001 in FIG. 14A havedifferent structures. Other common components are denoted by the samereference numerals in FIGS. 14A and 14B.

First, an alloy film of an aluminum (Al), nickel (Ni), and lanthanum(La) (Al—Ni—La alloy film) with a thickness of 200 nm was deposited overa glass substrate 4000 by a sputtering method, a film of Ti with athickness of 6 nm was deposited by a sputtering method, and then a filmof indium tin oxide containing silicon oxide (ITSO) with a thickness of40 nm was deposited by a sputtering method. As a result, the firstelectrode 4001 of each of Light-emitting Element 3 and ComparativeLight-emitting Element 4, which functions as an anode, was formed (FIG.14A). In each of Light-emitting Element 5 and Comparative Light-emittingElement 6, an alloy film of an aluminum (Al), nickel (Ni), and lanthanum(La) (Al—Ni—La alloy film) with a thickness of 200 nm was deposited overthe substrate 4000 by a sputtering method, a film of Ti with a thicknessof 6 nm was deposited by a sputtering method, and then indium tin oxidecontaining silicon oxide (ITSO) with a thickness of 75 nm was depositedby a sputtering method, whereby the first electrode 4101, whichfunctions as an anode, was formed. At this time, the films of Ti werepartially or entirely oxidized and contained titanium oxide. Note thatthe electrode area was 2 mm×2 mm.

Then, as pretreatment for forming Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6 over the substrate 4000, UV ozone treatment wasperformed for 370 seconds after washing of a surface of the substratewith water and 1-hour baking at 200° C.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 60 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 4000 was cooled down for about 30 minutes.

Next, the substrate 4000 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 4000 providedwith the first electrodes (4001 and 4101) was directed downward. In thisexample, by a vacuum evaporation method, a first hole-injection layer4011 a, a first hole-transport layer 4012 a, a light-emitting layer (A)(4013 a), a first electron-transport layer 4014 a, and a firstelectron-injection layer 4015 a, which are included in a first EL layer4002 a, were sequentially formed, and then a charge generation layer4004 was formed. After that, a second hole-injection layer 4011 b, asecond hole-transport layer 4012 b, a light-emitting layer (B) (4013 bor 4013 b′), a second electron-transport layer (4014 b, 4014 b′), and asecond electron-injection layer 4015 b, which are included in a secondEL layer 4002 b, were sequentially formed.

After reducing the pressure in the vacuum evaporation apparatus to 10⁻⁴Pa, 9-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]phenanthrene (abbreviation:PcPPn) and molybdenum oxide were co-evaporated at a mass ratio of 1:0.5(PcPPn (abbreviation):molybdenum oxide), whereby the firsthole-injection layer 4011 a was formed over each of the first electrodes(4001 and 4101). Note that co-evaporation is an evaporation method inwhich some different substances are evaporated from some differentevaporation sources at the same time. The thicknesses of the firsthole-injection layer 4011 a were 13.5 nm, 10 nm, 21 nm, and 10 nm in thecase of Light-emitting Element 3, Comparative Light-emitting Element 4,Light-emitting Element 5, and Comparative Light-emitting Element 6,respectively.

Then, PcPPn (abbreviation) was deposited by evaporation, so that thefirst hole-transport layer 4012 a was formed. The thicknesses of thefirst hole-transport layer 4012 a were 10 nm, 15 nm, 10 nm, and 15 nm inthe case of Light-emitting Element 3, Comparative Light-emitting Element4, Light-emitting Element 5, and Comparative Light-emitting Element 6,respectively.

Next, a light-emitting layer (A) 4013 a was formed over the firsthole-transport layer 4012 a. The light-emitting layer (A) 4013 a wasformed by co-evaporation of9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA)andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) at a mass ratio of 1:0.05 (CzPA(abbreviation):1,6mMemFLPAPrn (abbreviation)). The thickness thereof wasset to 25 nm.

Next, the first electron-transport layer 4014 a was formed over thelight-emitting layer (A) 4013 a in such a manner that a film of CzPA(abbreviation) was deposited by evaporation to a thickness of 5 nm andthen a film of bathophenanthroline (abbreviation: BPhen) was depositedby evaporation to a thickness of 15 nm. In addition, lithium oxide(Li₂O) was deposited by evaporation to a thickness of 0.1 nm over thefirst electron-transport layer 4014 a, whereby the firstelectron-injection layer 4015 a was formed.

Then, copper phthalocyanine (abbreviation: CuPc) was deposited byevaporation to a thickness of 2 nm over the first electron-injectionlayer 4015 a, whereby the charge generation layer 4004 was formed.

Next, over the charge generation layer 4004,1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum oxide were co-evaporated to a thickness of 12.5 nm at a massratio of 1:0.5 (DBT3P-II (abbreviation):molybdenum oxide), whereby thesecond hole-injection layer 4011 b was formed.

Then, the second hole-transport layer 4012 b was formed by depositingBPAFLP (abbreviation) by evaporation to a thickness of 20 nm.

Next, the light-emitting layer (B) (4013 b, 4013 b′) was formed over thesecond hole-transport layer 4012 b.

The light-emitting layer (B) 4013 b included in each of Light-emittingElement 3 and Light-emitting Element 5 (light-emitting elements on theleft sides of FIGS. 14A and 14B) has a stacked-layer structure of threelayers of a first light-emitting layer 4013(b 1), a secondlight-emitting layer 4013(b 2), and a third light-emitting layer 4013(b3).

The first light-emitting layer 4013(b 1) was formed to have a thicknessof 20 nm by co-evaporating2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF), and(Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) at a mass ratio of 0.8:0.2:0.06(2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]).

The second light-emitting layer 4013(b 2) was formed to have a thicknessof 10 nm by co-evaporating 2mDBTBPDBq-II (abbreviation), PCBBiF(abbreviation), andbis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-dmp)₂(acac)]) at a mass ratio of 0.9:0.1:0.06(2mDBTBPDBq-II:PCBBiF:[ft(dmdppr-dmp)₂(acac)]).

The third light-emitting layer 4013(b 3) was formed to have a thicknessof 10 nm by co-evaporating 2mDBTBPDBq-II (abbreviation), PCBBiF(abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) at a mass ratioof 0.8:0.2:0.06 (2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)].

The light-emitting layer (B) 4013 b′ has a stacked-layer structure oftwo layers of a first light-emitting layer 4013(b1′) and a secondlight-emitting layer 4013(b2′) included in Comparative Light-emittingElement 4 and Comparative Light-emitting. Element 6 (light-emittingelements on the right sides of FIGS. 14A and 14B).

The first light-emitting layer 4013(b1′) was formed to have a thicknessof 20 nm by co-evaporating 2mDBTBPDBq-II (abbreviation), PCBBiF(abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) at a mass ratioof 0.8:0.2:0.06 (2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]).

The second light-emitting layer 4013(b2′) was formed to have a thicknessof 20 nm by co-evaporating 2mDBTBPDBq-II (abbreviation) and[Ir(dmdppr-dmp)₂(acac)] (abbreviation) at a mass ratio of 1:0.06(2mDBTBPDBq-II:[Ir(dmdppr-dmp)₂(acac)]).

Next, the second electron-transport layer (4014 b, 4014 b′) was formedover the light-emitting layer (B) (4013 b, 4013 b′).

Next, the second electron-transport layer 4014 b included in each ofLight-emitting Element 3 and Light-emitting Element 5 (light-emittingelements on the left sides of FIGS. 14A and 14B) was formed in such amanner that a film of 2mDBTPDBq-II (abbreviation) was deposited byevaporation to a thickness of 30 nm and then a film of BPhen(abbreviation) was deposited by evaporation to a thickness of 15 nm.Furthermore, the second electron-transport layer 4014 b′ included ineach of Light-emitting Element 4 and Light-emitting Element 6(light-emitting elements on the right sides of FIGS. 14A and 14B) wasformed in such a manner that a film of 2mDBTPDBq-II (abbreviation) wasdeposited by evaporation to a thickness of 35 nm and then a film ofBPhen (abbreviation) was deposited by evaporation to a thickness of 15nm.

In addition, a film of lithium fluoride (LiF) was formed by evaporationto a thickness of 1 nm, whereby the second electron-injection layer 4015b was formed over the second electron-transport layers (4014 b and 4014b′).

Finally, the second electrode 4003 serving as a cathode was formed overthe second electron-injection layer 4015 b. The second electrode 4003was obtained in such a manner that silver (Ag) and magnesium (Mg) weredeposited by co-evaporation at a mass ratio of 1:0.1 to a thickness of15 nm and then indium tin oxide (ITO) was deposited to a thickness of 70nm by a sputtering method. Note that in all the above evaporation steps,evaporation was performed by a resistance heating method.

Element structures of Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6 obtained through the above steps are shown inTable 3.

TABLE 3 First hole- First hole- Light-emitting First electron- Firstelectrode injection layer transport layer layer (A) transport layerLight- Al—Ni—La\Ti NITO PCPPn:MoOx PCPPn * CzPA Bphen emitting (200 nm\6nm) (40 nm) (1:0.5 13.5 nm) (10 nm) (5 nm) (15 nm) Element 3 ComparativePCPPn:MoOx PCPPn Light- (1:0.5 10 nm) (15 nm) emitting Element 4 Light-NITO PCPPn:MoOx PCPPn emitting (75 nm) (1:0.5 21 nm) (10 nm) Element 5Comparative PCPPn:MoOx PCPPn Light- (1:0.5 10 nm) (15 nm) emittingElement 6 Charge- Light-emitting layer (B) First electron- generationSecond hole- Second hole- 1st 2nd 3rd injection layer layer injectionlayer transport layer 1st 2nd Light- Li₂O CuPc DBT3P-II:MoOx BPAFLP ***** **** emitting (0.1 nm) (2 nm) (1:0.5 12.5 nm) (20 nm) Element 3Comparative ***** Light- emitting Element 4 Light- *** **** emittingElement 5 Comparative ***** Light- emitting Element 6 Second electron-Second electron- transport layer injection layer Second electrode CFLight- 2mDBTBPDBq-II Bphen LiF Ag:Mg ITO G emitting (30 nm) (15 nm) (1nm) (1:0.1 15 nm) (70 nm) Element 3 Comparative 2mDBTBPDBq-II Light- (35nm) emitting Element 4 Light- 2mDBTBPDBq-II R emitting (30 nm) Element 5Comparative 2mDBTBPDBq-II Light- (35 nm) emitting Element 6 *CzPA:1,6mMemFLPAPrn (1:0.05 25 nm) **2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.06 20 nm) ***2mDBTBPDBq-II:PCBBiF:[Ir(dmdppr-dmp)₂(acac)] (0.9:0.1:0.06 10 nm) ****2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.06 10 nm) *****2mDBTBPDBq-II:[Ir(dmdppr-dmp)₂(acac)] (1:0.06 20 nm)

As shown in Table 3, a green coloring layer (G) was formed in a countersubstrate of Light-emitting Element 3 and Comparative Light-emittingElement 4, and a red coloring layer (R) was formed in a countersubstrate of Light-emitting Element 5 and Comparative Light-emittingElement 6. The fabricated Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6 were sealed by being bonded to these countersubstrates in a glove box containing a nitrogen atmosphere so as not tobe exposed to the air (specifically, a sealant was applied onto an outeredge of the element, and the sealant was irradiated with ultravioletlight with a wavelength of 365 nm at 6 J/cm² and heat treatment wasperformed at 80° C. for 1 hour at the time of sealing).

<<Operation Characteristics of Light-Emitting Element 3, ComparativeLight-Emitting Element 4, Light-Emitting Element 5, and ComparativeLight-Emitting Element 6>>

Operation characteristics of Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6 were evaluated. Note that the measurement wascarried out at room temperature (under an atmosphere in which thetemperature was kept at 25° C.). In FIG. 15, to the numbers of elementsin a legend, (G) and (R) are added in the case of the light-emittingelement that emits green light and in the case of the light-emittingelement that emits red light, respectively, to show the light-emittingcolor of each light-emitting element. Moreover, the same applies to FIG.17.

First, FIG. 15 shows luminance-current efficiency characteristics ofLight-emitting Element 3, Comparative Light-emitting Element 4,Light-emitting Element 5, and Comparative Light-emitting Element 6. InFIG. 15, the vertical axis represents current efficiency (cd/A) and thehorizontal axis represents luminance (cd/m²). Furthermore, FIG. 16 showsvoltage-luminance characteristics of Light-emitting Element 3,Comparative Light-emitting Element 4, Light-emitting Element 5, andComparative Light-emitting Element 6. In FIG. 16, the vertical axisrepresents luminance (cd/m²) and the horizontal axis represents voltage(V).

Table 4 shows initial values of main characteristics of Light-emittingElement 3, Comparative Light-emitting Element 4, Light-emitting Element5, and Comparative Light-emitting Element 6 at a luminance ofapproximately 1000 cd/m².

TABLE 4 Current Current Voltage Current density Chromaticity Luminanceefficiency (V) (mA) (mA/cm²) (x, y) (cd/m²) (cd/A) Light- 6.2 0.06 1.5(0.27, 0.71) 970 65 emitting Element 3 Comparative 6.4 0.077 1.9 (0.26,0.72) 1100 55 Light- emitting Element 4 Light- 7.0 0.27 6.8 (0.67, 0.33)1100 16 emitting Element 5 Comparative 7.2 0.25 6.2 (0.67, 0.33) 1100 17Light- emitting Element 6

From the above results, it can be found that Light-emitting Element 3and Comparative Light-emitting Element 4 fabricated in this example emitgreen (G) light, and Light-emitting Element 5 and ComparativeLight-emitting Element 6 fabricated in this example emit red (R) light,which is clearly different from green light. Thus, these light-emittingelements are used in appropriate combination, whereby full-color displaycan be fabricated.

FIG. 17 shows emission spectra when a current with a current density of2.5 mA/cm² was supplied to Light-emitting Element 3, ComparativeLight-emitting Element 4, Light-emitting Element 5, and ComparativeLight-emitting Element 6. As shown in FIG. 17, the emission spectra ofLight-emitting Element 3 and Comparative Light-emitting Element 4 bothhave peaks at approximately 536 nm, and the emission spectra ofLight-emitting Element 5 and Comparative Light-emitting Element 6 bothhave peaks at approximately 616 nm, which indicates that the peak ofeach light-emitting element is attributed to light emission from aphosphorescent organometallic iridium complex included in eachlight-emitting layer.

When Light-emitting Element 3 and Comparative Light-emitting Element 4each of which emits green light are compared with each other, althoughthe current efficiency of Light-emitting Element 3(G) is higher thanthat of Comparative Light-emitting Element 4(G) in FIG. 15, the peak ofemission spectrum of Light-emitting Element 3(G) is near to a wavelengthof 550 nm, which is the wavelength with high luminosity in FIG. 17.These results suggest that the current efficiencies of Light-emittingElement 3(G) and Comparative Light-emitting Element 4(G) are almost thesame with the same chromaticity. When Light-emitting Element 5 andComparative Light-emitting Element 6 each of which emits red light arecompared with each other, although the current efficiency ofLight-emitting Element 5(R) is lower than that of ComparativeLight-emitting Element 6(R) in FIG. 15, the emission spectrum ofLight-emitting Element 5(R) is observed on the side of long wavelengths,which is the wavelength side with low luminosity in FIG. 17. Thus, thecurrent efficiencies of Light-emitting Element 5(R) and ComparativeLight-emitting Element 6(R) are the same when the light path lengths arepresumably optimized. That is, Light-emitting Element 3 andLight-emitting Element 5 have initial characteristics similar to thoseof Comparative Light-emitting Element 4 and Comparative Light-emittingElement 6.

FIG. 18 shows results of reliability tests of Light-emitting Element 3,Comparative Light-emitting Element 4, Light-emitting Element 5, andComparative Light-emitting Element 6. In FIG. 18, the vertical axisrepresents normalized luminance (%) when an initial luminance is 100%and the horizontal axis represents driving time (h) of the element. Notethat in the reliability tests, Light-emitting Element 3 and ComparativeLight-emitting Element 4 were driven under the conditions where theinitial luminance was set to 1667 cd/m² and the current density wasconstant, and Light-emitting Element 5 and Comparative Light-emittingElement 6 were driven under the conditions where the initial luminancewas set to 655 cd/m² and the current density was constant. As a result,it is found that when the light-emitting layer (B) has a stacked-layerstructure of three layers like in Light-emitting Element 3 andLight-emitting Element 5, in the case of Light-emitting Element 3 thatemits green light, a rapid reduction in luminance in the initial stageof driving can be suppressed compared with Comparative Light-emittingElement 4 that also emits green light. Moreover, in the case ofLight-emitting Element 5 that emits red light, a rapid increase inluminance in the initial stage of driving can be suppressed comparedwith Comparative Light-emitting Element 6 that also emits red light.

Note that the combination of 2mDBTBPDBq-II (abbreviation) and PCBBiF(abbreviation), which are used for the light-emitting layers (B) 4013 bof Light-emitting Element 3 and Light-emitting Element 5 in thisexample, forms an exciplex.

Example 3

In this example, a 3.4-inch active matrix display fabricated using thelight-emitting element of one embodiment of the present invention isdescribed. In this 3.4-inch active matrix display, light-emitting layersin light-emitting elements have the same structures as thelight-emitting layers of Light-emitting Element 3 and Light-emittingElement 5 in Example 2.

For a driver circuit portion of this 3.4-inch active matrix display, anFET using an oxide semiconductor was used.

Main specifications and characteristics of the fabricated 3.4-inchactive matrix display are shown in Table 5 below.

TABLE 5 Aper- OLED Emis- Screen Driving Pixel ture Struc- Coloring sionNTSC Pixel Scan Source Diagonal Method Resolution Pixel Size DensityRatio ture Method Type ratio Circuit Driver Driver 3.4-inch Active 960 ×(RGB) × 540 26 μm × 78 μm 326 ppi 44% B\GRG White Top >90% 3Tr + 1C/Inte- SSD Matrix (Quarter-FHD) OLED + emis- pixel grated Color sionFilter * designed value

Moreover, FIG. 19 shows the measurement results of this display for achange in chromaticity over time when this display was continuouslydriven while emitting white light of 300 [cd/m²] (chromaticity atapproximately D65). From these results, it is found that the 3.4-inchactive matrix display using light-emitting elements with the samestructures as Light-emitting Element 3 and Light-emitting Element 5 inExample 2 has a small change in chromaticity over time likeLight-emitting Element 3 and Light-emitting Element 5.

Example 4

In this example, Light-emitting Element 3 having the same structure asLight-emitting Element 3 in Example 2 and Light-emitting Element 5having the same structure as Light-emitting Element 5 in Example 2 werefabricated, and the analysis results thereof by time-of-flight secondaryion mass spectrometry (ToF-SIMS) in the depth direction are shown.TOF.SIMS 5 (manufactured by ION-TOF GmbH) was used, and the analysis wasperformed using Bi as a primary ion source at less than or equal to 1E12(ions/cm²) in a positive mode. Furthermore, on each light-emittingelement from which a second electrode (cathode) had been removed, theanalysis was performed from the second electrode side to the firstelectrode side while digging was performed using GCIB (Ar cluster) as asputtering ion source.

<ToF-SIMS in Depth Direction>

FIGS. 20A and 20B show results obtained by analysis of a region aroundthe light-emitting layer (B) to the second electron-transport layer inLight-emitting Element 3 by the ToF-SIMS. The analysis results ofLight-emitting Element 5 are shown in FIGS. 21A and 21B. In each graph,the vertical axis represents normalized secondary ion intensity and thehorizontal axis represents depth, and 0 cycles indicates the start ofdigging. Thus, here, 0 cycles indicates a region around the secondelectron-injection layer on the cathode side. The scales of thehorizontal axes in the figures (A) and (B) of the same element are thesame. FIGS. 20A and 21A of these graphs show the secondary ion intensitywhen m/z=615, m/z=714, m/z=976, and m/z=1074. In addition, FIGS. 20B and21B show the secondary ion intensity when m/z=565 and m/z=678.

From FIGS. 20A and 21A, it is found that profiles of m/z=615 and m/z=714are similar to each other, and profiles of m/z=976 and m/z=1074 aresimilar to each other. Thus, it is suggested that m/z=714 is themass-to-charge ratio mainly attributed to [Ir(tBuppm)₂(acac)], m/z=615is the mass-to-charge ratio mainly attributed to a product ion that isformed by removing an acetylacetone group from [Ir(tBuppm)₂(acac)],m/z=1074 is the mass-to-charge ratio mainly attributed to[Ir(dmdppr-dmp)₂(acac)], and m/z=976 is the mass-to-charge ratio mainlyattributed to a product ion that is formed by removing an acetylacetonegroup from [Ir(dmdppr-dmp)₂(acac)]. In addition, profiles of m/z=384 andm/z=599 are similar to that of m/z=714; thus it is suggested that themass-to-charge ratios each of which is also mainly attributed to aproduct ion of [Ir(tBuppm)₂(acac)] are detected. Moreover, a profile ofm/z=976 is similar to that of m/z=1074; thus, it is suggested that themass-to-charge ratio which is also mainly attributed to a product ion of[Ir(dmdppr-dmp)₂(acac)] is detected.

Furthermore, from profiles and mass-to-charge ratios of FIGS. 20B and21B, it is suggested that m/z=565 is the mass-to-charge ratio which ismainly attributed to 2mDBTBPDBq-II, and m/z=678 is the mass-to-chargeratio which is mainly attributed to a product ion of PCBBiF. Inaddition, profiles of m/z=176 and m/z=201 are similar to that ofm/z=565; thus, it is suggested that the mass-to-charge ratios each ofwhich is also mainly attributed to a product ion of 2mDBTBPDBq-II aredetected.

In FIG. 20A that shows the analysis results of Light-emitting Element 3,an ion has two peaks attributed to [Ir(tBuppm)₂(acac)], and a peakattributed to [Ir(dmdppr-dmp)₂(acac)] is shown between these peaks. Onthe other hand, in FIG. 21A that shows the analysis results ofLight-emitting Element 5, it is observed that a peak attributed to[Ir(dmdppr-dmp)₂(acac)] is adjacent to a peak attributed to[Ir(tBuppm)₂(acac)]. From these results, it is found that a profile ofeven a thin film with a thickness of 10 nm to 20 nm can be observed byan analysis method using the ToF-SIMS.

From FIGS. 20A, 20B, 21A, and 21B, it is found that ions contained inthe element structure can be analyzed by the ToF-SIMS. Moreover, it isfound that profiles of ions of a substance contained in a stacked filmof other layers (the first hole-injection layer to the secondhole-transport layer) can be obtained in the stacking order and analyzedby the ToF-SIMS.

<ToF-SIMS of Light-Emitting Layer>

Next, regions around the third light-emitting layer (4013(b 3)), thesecond light-emitting layer (4013(b 2)), and the first light-emittinglayer (4013(b 1)) of the light-emitting layer (B) 4013 b ofLight-emitting Element 3 are each measured, and FIGS. 22A, 22B, and 22Cshow the measurement results around the third light-emitting layer(4013(b 3)), the measurement results around the second light-emittinglayer (4013(b 2)), and the measurement results around the firstlight-emitting layer (4013(b 1)) of the light-emitting layer (B) 4013 b,respectively. FIG. 22A, FIG. 22B, and FIG. 22C correspond to theintegral detection intensity in a 37 to 38 cycle portion, the integraldetection intensity in a 46 to 47 cycle portion, and the integraldetection intensity in a 58 to 59 cycle portion in FIGS. 20A and 20B,respectively. In FIGS. 22A to 22C, the vertical axis representssecondary ion intensity, and the horizontal axis representsmass-to-charge ratio.

FIG. 23A shows the measurement results by the ToF-SIMS around the secondlight-emitting layer (4013(b 2)) and the third light-emitting layer(4013(b 3)) of the light-emitting layer (B) 4013 b of Light-emittingElement 5, and FIG. 23B shows the measurement results by the ToF-SIMSaround the first light-emitting layer (4013(b 1)) of the light-emittinglayer (B) 4013 b of Light-emitting Element 5. FIG. 23A and FIG. 23Bcorrespond to the integral detection intensity in a 45 to 46 cycleportion and the integral detection intensity in a 63 to 64 cycle portionin FIGS. 21A and 21B, respectively. In FIGS. 23A and 23B, the verticalaxis represents secondary ion intensity, and the horizontal axisrepresents mass-to-charge ratio.

In FIG. 22A, FIG. 22C, and FIG. 23B, m/z=714, m/z=615, and m/z=599attributed to [Ir(tBuppm)₂(acac)] and m/z=678 attributed to PCBBiF areobserved. Furthermore, in FIG. 22B and FIG. 23A, m/z=1074 and m/z=976attributed to [Ir(dmdppr-dmp)₂(acac)] are observed.

<ToF-SIMS of Single Film>

Next, a single film of [Ir(tBuppm)₂(acac)] included in the firstlight-emitting layer (4013(b 1)) and the third light-emitting layer(4013(b 3)) of the light-emitting layer (B) 4013 b of Light-emittingElement 3 was formed by an evaporation method, and measurement wasperformed on the single film by the ToF-SIMS. FIG. 24 shows themeasurement results. In FIG. 24, the vertical axis represents secondaryion intensity, and the horizontal axis represents mass-to-charge ratio.

From FIG. 24, it is found that m/z=714, m/z=615, and m/z=599, which arepeaks attributed to [Ir(tBuppm)₂(acac)], are observed at the sameproduct peak pattern as those in FIG. 22A, FIG. 22C, and FIG. 23B.

Note that in the case of a mixed film, when there is a mass-to-chargeratio that is the same as that of an ion of another material, the peaksoverlap with each other and the intensity ratio might be changed; thus,attention needs to be paid.

From the above analysis results of the ToF-SIMS, it is found that in thesubstance contained in the light-emitting element, a product ion can besensitively analyzed as in the case of the single film. Moreover, it isfound that even in a sample with a low proportion of the substances anda sample with a thin film, a product ion can be analyzed by theToF-SIMS.

In the case of a complex that is often used as a dopant in alight-emitting layer, a product ion with a structure from which oneligand is removed (mass-to-charge ratio: (P)/z) can be sensitivelyanalyzed. The mass-to-charge ratio to be obtained is represented by(Formula 1). In (Formula 1), (C) represents precise mass of complexmolecules, and (L) represents precise mass of ligands that aresubstituted. Note that (P)/z has a margin of error of plus or minus 2.

(P)/z=(C)-(L)  (Formula 1)

The ligand contained in the complex can have any of the followingstructures (Structural Formulae (100 to 111), (120 to 126), and (130 to186)), for example.

When a ligand represented by Structural Formula (100) (acetylacetone(abbreviation: acac)) is removed from a complex, a product ion having amass-to-charge ratio obtained by subtracting 99 from precise mass of thecomplex is easily detected. For example, when the complex is[Ir(tBuppm)₂(acac)] whose precise mass is 714, a product ion of m/z=615obtained by subtracting 99 from the precise mass is detected.Alternatively, when the complex is [Ir(dmdppr-dmp)₂(acac)] whose precisemass is 1074, a product ion of m/z=975 obtained by subtracting 99 fromthe precise mass is detected.

This indicates that a product ion formed by removing a chelate ligandsuch as a ligand represented by any of the above Structural Formulae(100) to (111) and Structural Formulae (120) to (126) from a complex iseasily detected. That is, this indicates that a product ion from whichsuch a chelate ligand is removed is easily detected as compared with aproduct ion from which a ligand forming a covalent bond with metal isremoved.

In the case of using a tris-type structure in which the same ligands arebonded to each other, a mass-to-charge ratio represented by thefollowing (Formula 2) is detected. Note that (M) represents the precisemass of a central metal, and n represents the number of ligands. Notethat (P)/z has a margin of error of plus or minus 2.

(P)/z={(C)−(M)}/n+(M)  (Formula 2)

As the central metal, iridium, platinum, silver, copper, aluminum,ruthenium, cobalt, iron, gallium, hafnium, lithium, nickel, tin,titanium, vanadium, zinc, or the like can be used.

Thus, a complex and an inorganic compound such as molybdenum oxide,lithium, and a lithium compound are preferably used, because they can beanalyzed more easily when the SIMS analysis in the depth direction isalso performed.

This application is based on Japanese Patent Application serial no.2013-215721 filed with Japan Patent Office on Oct. 16, 2013, andJapanese Patent Application serial no. 2014-101204 filed with JapanPatent Office on May 15, 2014, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. A light-emitting device comprising: a firstelectrode; a first light-emitting layer over the first electrode andcomprising a first light-emitting material and a first organic compound;a second light-emitting layer over the first light-emitting layer andcomprising a second light-emitting material and a second organiccompound; a third light-emitting layer over the second light-emittinglayer and comprising the first light-emitting material and a thirdorganic compound; and a second electrode over the third light-emittinglayer, wherein: the first light-emitting material and the secondlight-emitting material are different from each other, the firstlight-emitting layer and the third light-emitting layer exhibit firstemission, second emission from the second light-emitting layer has anemission peak at a longer wavelength than the first emission, and thefirst light-emitting layer comprises the first organic compound and afourth organic compound which form an exciplex, the secondlight-emitting layer comprises the second organic compound and a fifthorganic compound which form an exciplex, and the third light-emittinglayer comprises the third organic compound and a sixth organic compoundwhich form an exciplex.
 2. The light-emitting device according to claim1, wherein: the first organic compound is different from the firstlight-emitting material, the second organic compound is different fromthe second light-emitting material, and the third organic compound isdifferent from the first light-emitting material.
 3. The light-emittingdevice according to claim 1, wherein: each of the first organiccompound, the second organic compound, and the third organic compoundhas hole-transport property, and each of the fourth organic compound,the fifth organic compound, and the sixth organic compound haselectron-transport property.
 4. The light-emitting device according toclaim 1, wherein at least one of the first emission and the secondemission is phosphorescence.
 5. The light-emitting device according toclaim 1, wherein: the first emission is green light, and the secondemission is red light.
 6. The light-emitting device according to claim1, wherein the first light-emitting material and the secondlight-emitting material individually are any one of a substance emittingfluorescence, a substance emitting phosphorescence and a thermallyactivated delayed fluorescence material.
 7. The light-emitting deviceaccording to claim 1, wherein: the first organic compound, the secondorganic compound, and the third organic compound are the same as eachother, and the fourth organic compound, the fifth organic compound, andthe sixth organic compound are the same as each other.
 8. An electronicdevice comprising the light-emitting device according to claim
 1. 9. Alighting device comprising the light-emitting device according toclaim
 1. 10. A light-emitting device comprising: a first electrode; afirst light-emitting layer over the first electrode and comprising afirst light-emitting material and a first organic compound; a secondlight-emitting layer over the first light-emitting layer and comprisinga second light-emitting material and a second organic compound; a thirdlight-emitting layer over the second light-emitting layer and comprisingthe first light-emitting material and a third organic compound; and asecond electrode over the third light-emitting layer, wherein: the firstlight-emitting material and the second light-emitting material aredifferent from each other, the first light-emitting layer and the thirdlight-emitting layer exhibit first emission, second emission from thesecond light-emitting layer has an emission peak at a longer wavelengththan the first emission, and the first emission is green light.
 11. Thelight-emitting device according to claim 10, wherein: the first organiccompound is different from the first light-emitting material, the secondorganic compound is different from the second light-emitting material,and the third organic compound is different from the firstlight-emitting material.
 12. The light-emitting device according toclaim 10, wherein each of the first organic compound, the second organiccompound, and the third organic compound has hole-transport property,and
 13. The light-emitting device according to claim 10, wherein atleast one of the first emission and the second emission isphosphorescence.
 14. The light-emitting device according to claim 10,wherein the first light-emitting material and the second light-emittingmaterial individually are any one of a substance emitting fluorescence,a substance emitting phosphorescence and a thermally activated delayedfluorescence material.
 15. The light-emitting device according to claim10, wherein the first organic compound, the second organic compound, andthe third organic compound are the same as each other.
 16. An electronicdevice comprising the light-emitting device according to claim
 10. 17. Alighting device comprising the light-emitting device according to claim10.